An injection system of the “hot runner” type usually includes:
a manifold delimiting a distribution channel for thermoplastic material and including a thermoplastic material outlet,
an injection nozzle defining at least a portion of a transit passage the entrance whereof is fluidically connected with the outlet of the distribution channel, and the outlet whereof opens substantially into the mold cavity,
a nozzle gate mounted so as to slide longitudinally within the transit passage and alternately occupying a position closing said passage and a position opening it,
control means for causing the nozzle gate to slide alternately between the closing position and the opening position.
The control means typically include a power cylinder connected to the nozzle gate. This type of injection system additionally includes supply means capable of supplying the manifold with material to be injected.
To satisfactorily inject the material into the cavity, the material must be maintained in the fluid state, this state being obtained when the material is brought to a predetermined final temperature greater than the temperature of the ambient air. To this end, the manifold includes, in known fashion, means allowing the temperature thereof, and consequently that of the material passing through its distribution channel, to be maintained at a temperature greater than the fusion temperature of the material. The material in the fluid state is inserted into the distribution channel by the supply means and enters the transit passage of the injection nozzle.
When the control means bring the nozzle gate into the closing position, the nozzle outlet is closed and the material to be injected is retained in the transit passage. When the control means bring the nozzle gate into the open position, the nozzle outlet is open and the material is injected into the cavity. Conventionally, said control means are located in the ambient air on the face of the manifold longitudinally opposite to the molding cavity (or “back face” of the manifold).
Now, as the manifold is maintained at an elevated temperature, it is indispensable to provide cooling for the power cylinder. This cooling is typically obtained by means of water circulation around the power cylinder. Now the placement of this water circuit is problematic because it complicates the injection system and is relatively costly. In addition, the thickness of the power cylinder contributes to a considerable increase in thickness of the injection system.
One of the objects of the invention is therefore to design an injection system in which the cooling of the nozzle gate control means can be dispensed with. Another object of the invention is to minimize the total thickness of the injection system.